1. What is the most important lesion produced in chromosomal DNA by exposure to ionizing radiation?

a. A break on one DNA strand ('single-strand break').

b. Well-separated breaks on both DNA strands.

c. Breaks on both DNA strands which are opposite each other or separated by only a few bases ('double-strand break').

d. Multiple breaks on the same DNA strand.

2. When cells are irradiated with x-rays, double-strand breaks occur at a rate of about 5% in comparison to single-strand breaks.

a. True.

b. False.

3. Which of the following statements is correct?

a. Double-strand breaks can be repaired by homologeous recombination or nonhomologous recombination.

b. Nonhomologous recombination is error-free.

c. Homologous recombination occurs often in mammalian cells.

d. Homologous recombination accounts for many of the premutagenic lesions induced in the DNA of human cells by ionizing radiation.

4. Which of the following statements is false?

a. 95% of the energy deposition of x-rays and gamma rays occurs in spurs (which have a diameter of about 4 nm and involve 3 ion pairs on average).

b. Spurs and blobs are equally frequent in the case of high energy gamma rays.

c. Blobs have a diameter of about 7 nm and contain 12 ion pairs on average.

d. As spurs and blobs have a diameter similar to the DNA diameter, complex lesions occur when they overlap with the DNA helix ('locally multiply damaged site').

5. The D₀ dose is the dose that:

a. induces an average of one lethal event per cell and leaves 37% still viable.

b. leaves 50% of all cells viable.

c. kills all cells.

d. kills 30% of all cells.

6. Chromosomal aberrations are caused by:

a. single-strands breaks.

b. double-strand breaks, i.e. breaks that cause the chromatin to snap into two pieces.

c. single-strand or double-strand breaks.

7. Following exposure to radiation, some of the chromatin strands are broken. Broken ends are "sticky" and can join to other broken "sticky" ends. Which of the following statements is false?

a. Broken ends of the same chromatin can recombine to restore the original structure of the chromosome.

b. The broken end of one chromatin strand can join to the broken end of another chromatin strand (which leads to a chromosomal aberration)

c. Broken ends fail to rejoin (which leads to a chromosomal aberration).

d. A broken end of a chromatin strand joins to an unbroken end of another chromatin strand.

8. The chromosome material is duplicated at:

a. prophase.

b. metaphase.

c. interphase.

d. anaphase.

9. Which of the following statements is false?

a. Chromosomal aberrations are divided into "chromosome aberrations" and "chromatid aberrations".

b. Chromosome aberrations are caused by irradiation that takes place before the DNA is duplicated.

c. Chromatid aberrations are caused by irradiation that takes place after the DNA is duplicated.

d. Chromatid aberrations involve identical breaks in the two strands of chromatin of the duplicated DNA structure.

10. Which of the following statements is false?

a. Chromosomal aberrations can lead to cell killing, mutation or carcinogenesis.

b. The ring aberration and the dicentric aberration are chromatid aberrations that are lethal to the cell.

c. The anaphase bridge is a chromosomal aberration that is lethal to the cell.

d. Symmetric translocations and small deletions are chromosomal aberrations that are not lethal but they can cause malignancies.

11. Which of the following statements is correct?

a. The total-body dose in exposed persons can be evaluated by taking blood samples and scoring the frequency of dicentrics and rings in the lymphocytes one year after exposure.

b. The total-body dose in exposed persons can be evaluated by taking blood samples and scoring the frequency of translocations in the lymphocytes up to several years after exposure.